Group III-V compound semiconductors, such as GaN and AlGaN, have many advantages, such as wide and easily controllable band gap energy, and are thus widely used for optoelectronics and electronics.
In particular, light emitting devices, such as light emitting diodes or laser diodes, which use group III-V or II-VI compound semiconductors, are capable of emitting visible and ultraviolet light of various colors such as red, green, and blue owing to development of device materials and thin film growth techniques. These light emitting devices are also capable of emitting white light with high luminous efficacy through use of a fluorescent substance or color combination and have several advantages of low power consumption, semi-permanent lifespan, fast response speed, safety, and environmental friendliness, as compared to conventional light sources, such as, fluorescent lamps and incandescent lamps.
Accordingly, application of the light emitting devices has been extended to transmission modules of optical communication means, light emitting diode backlights to replace Cold Cathode Fluorescent Lamps (CCFLs) which serve as backlights of Liquid Crystal Display (LCD) apparatuses, white light emitting diode lighting apparatuses to replace fluorescent lamps or incandescent lamps, vehicle headlights, and traffic lights.
A molding part to protect a light emitting structure or wires may be disposed around a light emitting device and, when light passes through the molding part formed of material, such as silicon, light is refracted by the molding part and the molding part may serve as a primary lens.
However, when a light emitting device is used as a light source of a lighting apparatus, a secondary lens to adjust the emission path of light may be used and the above-described secondary lens is generally referred as a ‘lens’.
A light path may be greatly changed according to materials of a lens, particularly, shapes of the lens, and, particularly, in the case of an application in which light emitted from a light source proceeds only in a specific direction, the shape of a lens is more important.